Cover sheets tightly with foil. Roast 15 minutes, then remove from oven. Remove foil, divide chicken between sheets, and continue to roast, rotating sheets top to bottom halfway through, until carrots are fork-tender, chicken is golden brown, and an instant-read thermometer inserted into the thickest part of a breast registers 165°F, 30–35 minutes (if some pieces of chicken are finished before others, transfer them to a serving platter).